The present invention concerns a suspension system for vehicles, in particular road vehicles. It concerns both the guiding of a vehicle wheel relative to the body of the vehicle, and the organisation of the suspension clearance movements of the wheel relative to the chassis. It relates more particularly to means used to control the position of the plane of the wheel, both in relation to the camber relative to the ground and in relation to the horizontal and vertical suspension movements relative to the body.
Control of the suspension clearance movements amounts to saying that the guiding must ensure a rigorously controlled position of the plane of the wheel relative to the chassis. In general, it is easy to define a longitudinal and vertical plane of symmetry on a vehicle. Let it be understood herein that the plane of symmetry serves as a reference plane related to the chassis. The guiding of the wheel plane aims to control as rigorously as possible the relative position of the wheel plane in relation to the chassis. It should be remembered that the xe2x80x9cplanexe2x80x9d of a wheel is the plane perpendicular to the rotation axis of the wheel, passing through the center of the ground contact area of a tire or an elastic hoop fitted on the wheel. It is convenient to use the term xe2x80x9cvertical suspensionxe2x80x9d for the clearance travel of the wheel vertically relative to the chassis. It is desirable to allow at least a slight movement in the longitudinal direction, and this is spoken of as the xe2x80x9chorizontal suspensionxe2x80x9d. The term xe2x80x9ccamberxe2x80x9d designates the angle xcex3 formed by the wheel plane relative to a line perpendicular to the ground. The term xe2x80x9csteeringxe2x80x9d is the rotation of the wheel plane about a perpendicular line extending upwards from the center of the tire""s ground contact area. Finally, xe2x80x9crollxe2x80x9d is the inclination of the vehicle body about a horizontal axis lying in the plane of symmetry (angle xcfx81).
The guiding of the wheel plane directly determines the position of the tire on the ground and hence also the stresses imposed on the tire and whether it is located in a more or less favourable position for the transmission of forces, in particular transverse forces. These forces are of prime importance for the handling of the vehicle, and therefore for safety.
The road vehicles in use now a days are known to undergo a rolling movement by virtue of their suspension. In effect, centrifugal force results in a load transfer towards the outside of the bend, whose consequence is that the suspensions on the side towards the outside of the bend are compressed more and those on the side towards the inside of the bend are relaxed, whence the roll. Owing to the increased camber of the wheel that it induces, this roll has an adverse effect both on passenger comfort and on the vehicle""s road-holding. The means most commonly used to combat roll is to use one or more anti-roll bars. Unfortunately, an anti-roll bar can only limit the roll by opposing it with a reaction moment. In principle it cannot prevent the onset of roll, and cannot therefore prevent the wheels from inclining in a direction unfavourable for proper operation of the tires.
The purpose of the invention is to provide a high level of vehicle operation safely and great comfort by means of suspension kinematics that enable simultaneous active control of the wheel""s camber and of the vertical suspension.
From U.S. Pat. No. 6,170,838 a proposal is already known, which describes a camber mechanism which, when viewed in a vertical plane perpendicular to the longitudinal axis of the vehicle, forms a parallelogram, combined with a horizontal suspension mechanism which also forms a parallelogram, this time when viewed in a horizontal plane. This enables extremely rigorous control of the wheel plane. However, the arrangement is fairly bulky, especially in its width.
The aim of the present invention is to provide a more compact arrangement which gives the same degrees of freedom of movement (and their rigorous control) of the wheel plane relative to the ground and relative to the chassis, while leaving more room available between the suspension mechanisms, in particular for the accommodation of the mechanical equipment and/or the passenger compartment.
The invention proposes a vehicle comprising:
a rolling and suspended chassis,
at least two ground contact systems, each comprising a wheel, the ground contact systems being mounted on the chassis transversely on either side thereof, the wheel of each ground contact system being mounted on a wheel carrier, the wheel carrier being mounted on a support by a vertical suspension device that ensures the vertical suspension travel movement of the wheel carrier relative to the support, the suspension travel movement taking place in the plane of the wheel and the suspension travel movement being sufficient to produce the required vertical suspension movement, the travel movement being controlled by appropriate means,
each support being mounted on the chassis in a manner enabling the plane of each wheel to be inclined relative to the chassis so as to impose on the planes of the wheels a camber angle xcex3 of a desired amplitude by inclining the wheels relative to the ground all on the same side, characterised in that
the support is mounted on the chassis by a load transfer arm on one side of which the support is articulated along an essentially horizontal geometrical camber axis, the load transfer arm being connected on its other side to the chassis along an essentially vertical geometrical axis,
a camber control rod being pivotally mounted on the support at some distance from the geometrical camber axis, the camber control rod being able to move transversely relative to the chassis,
a triangulation-forming element connecting the load transfer arm such that it controls the moment about the essentially vertical geometrical axis.
The expression xe2x80x9cground contact systemxe2x80x9d designates the totality of elements between the ground and the body or chassis of a vehicle. The invention proposes a suspension kinematic system as pure and complete as possible: the ground contact system provides not only vertical suspension, but also enables the camber of the wheel to be modified at any time but without reducing the vertical suspension path either on compression or on relaxation, while maintaining the vertical suspension in optimum operating condition in particular because control of the camber angle makes it possible to reduce the moments and shear stresses due to centrifugal force that appear in the vertical suspension while the vehicle is subjected to centrifugal forces. Of course, one cannot act directly upon the camber of a wheel relative to the ground; this is done indirectly, via a mechanism associated with the vehicle""s chassis.
According to a design variant, the invention proposes a vehicle with active roll control: the vehicle""s passenger compartment is mounted on the chassis such that it can incline towards the inside of a turn as a function of the centrifugal force. The passenger compartment is subjected to a roll which is more natural and better tolerated by the occupants of the vehicle, similar to conveyances with two aligned wheels (for example a motorcycle). It should be noted that although the roll is a phenomenon of the passenger compartment""s position relative to the ground, the roll angle is acted upon indirectly by acting between the chassis and the passenger compartment of the vehicle. The aim is to achieve a substantial variation range of the passenger compartment""s roll angle, of the same order of magnitude as the variation range of the camber. In that way, without necessarily reaching the roll angles that can be adopted by a vehicle with two aligned wheels, the effect produced is sufficiently perceptible to modify radically the impressions felt by the vehicle""s passengers and so to contribute to their comfort.
The invention will be better understood from the description below, relating to a vehicle with four wheels. The invention applies particularly to vehicles comprising at least four wheels, though the example given is not limiting.